1. Field of the Invention
The present invention relates generally to fastening devices, more particularly to ratchet buckles, strap tensioners, cargo restraining devices and the like used for tightening and tensioning a fastening strap for securing and restraining cargo loads or other objects.
2. Description of the Related Art
FIG. 1 shows a transport vehicle 11 carrying cargos or articles 12 secured by a plurality of fastening devices 2. The articles 12 being transported, normally stacked side by side and one above the other, are restrained from undesired movement or toppling down by the fastening devices 12. As shown in FIGS. 2 and 3, the fastening device 2 mainly comprises a lead strap 21, a lashing strap 22, a tightening and tensioning mechanism comprising a base 23 to which the lead strap 21 is attached and a lever 24 pivotally connected to the base 23 by a spindle formed by a pair of spindle components 25,26, and a pair of ratchet wheels 27 disposed around both ends of the spindle and rotatable in concert with the spindle components 25,26 when driven. A free end of the lashing strap 22 is attached to the spindle so as to be wound therearound. The ratchet wheels 27 each have a central hole which is separated into two semicircular openings, and the spindle components 25,26 are of semicircular cross section corresponding to the shape of the openings. The spindle components 25,26 are inserted into said openings, respectively, thus defining therebetween a gap for passage of a portion of the lashing strap 22. The lever 24 has a ratchet drive plate 241 for engaging and driving the ratchet wheels 27 to rotate in the winding direction of the lashing strap 22 when the lever 24 is pulled away from the base 24, and which is resiliently releasable from the ratchet wheels 27 when the lever 24 is pushed forward to the base 23 in the unwinding (reverse) direction, and the base 23 has a stop 231 that prevents the ratchet wheels 27 from rotating in the unwinding direction of the lashing strap 22 and that may be resiliently released from the ratchet wheels 27 when the ratchet wheels 27 are rotated in the winding direction. By such construction, the spindle components 25,26 can be rotated step by step to thereby incrementally shorten and tension the lashing strap 22.
In use, the articles 12 are preliminarily fastened with the lead and lashing straps 21,22, and then the lever 24 is repeatedly pulled back and forth, which causes the ratchet wheels 27 to drive the spindle components 25,26 to rotate in the winding direction of the lashing strap 22 thus incrementally shortening the length of the lashing strap 22. Accordingly, the lead and lashing straps 21,22 maintain the fastening tension and will not be loosened by the swaying motion of the transport vehicle, such that the objective of tightly fastening and restraining the articles 12 is achieved.
However, because the spindle components 25,26 are spaced-apart at a fixed distance due to the constraints of the ratchet wheels 27, the final angle/position of the spindle components 25,26, after being rotated in the winding direction to shorten the length of the lashing strap 22 for tensioning the articles 12, is unpredictable and usually only one of the spindle components 25,26 (i.e., the spindle component 26) bears the stress exerted along the tensioning direction. Even if both spindle components 25,26 bear the stress, the areas subjected to the stress are confined to the two edges 251,261 of the spindle components 25,26, respectively. Such stress concentration causes insufficiency in structural strength and easily predisposes the affected parts to twisting and deformation and even so far as causing fracture or breakage.